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WGU C839 Cryptography: Questions With A+ Solutions
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WGU C839 Cryptography: Questions With A+ Solutions
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WGU C839 Cryptography: Questions With A+ SolutionsKerckhoff's Principle Right Ans - A cryptosystem should be secure even if
everything about the system, except the key, is public knowledge.
Opposite of *security by obscurity*
Modern Cryptographic Algorithm Types Right Ans - Asymmetric and
Symmetric;
Combine substitution and transposition
Symmetric Cryptography Right Ans - Encryption that uses a *single key* to
encrypt and decrypt a message
Major issue is key exchange
C=E(k,p)
P=D(k,c)
Cryptographic *Substitution* Right Ans - Changing some part of the
plaintect for a matching part of the ciphertext.
All historical examples of crytpographic algorithms algorithms fall into this
category.
Cryptographic *Transposition* Right Ans - The swapping of blocks of
ciphertext.
Binary *OR* Right Ans - Asks if there is a 1 in the first number of the
second number, or in both, and returns a 1 if *TRUE*
1101
0110
1111 (result of OR)
, Binary *AND* Right Ans - Asks if there is a 1 in both the numbers and
returns a 1 if *TRUE*
1101
0110
0100 (result of AND)
Binary *XOR* Right Ans - Asks if there is a 1 in first number or the second
number, *but NOT in both* and returns 1 if *TRUE*
1101
0110
0101 (result of XOR)
Is reversible
Extensively used in modern cyrptography
Types of Symmetric Algorithms Right Ans - Block Ciphers and Stream
Ciphers
Block Ciphers Right Ans - Encrypts a message one block at a time
Usually 64-bit blocks, but newer algorithms (AES) use 128-bit blocks
Stream Ciphers Right Ans - Encrypt the data as a stream, one bit at a time
sub-key for the round Right Ans -
round function Right Ans -
Decryption (Feistel Function) Right Ans - SAME encryption function, but
keys/sub-keys in descending order!
Feistel Function Right Ans - AKA Feistel Cipher or Feistel Network
Invented by Horst Fesitel while working for IBM
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